A stereoscopic display presents different images to the left and right eyes of a viewer to enhance 3D perception. Stereo display may be accomplished, for example, using eye wear with passively polarized lenses or rapidly alternating shuttered glasses. However, such mechanisms burden a user with encumbrances which can block eye gaze or cover the user's face.
In contrast, an autostereoscopic (AS) display presents stereo imagery to a viewer without the need for special glasses. Three basic types of autostereoscopic displays include: holographic, volumetric, and parallax.
Holographic autostereoscopic displays may be produced by illuminating an object with coherent light (e.g., from a laser) and, without using lenses, exposing a film (or other medium) to light reflected from the object and to a direct beam of coherent light. When the interference patterns are then illuminated by the beam of coherent light, a three-dimensional image may be observed.
Volumetric autostereoscopic displays create 3-D imagery via the emission, scattering, or relaying of illumination from well-defined regions in (x,y,z) space. In volumetric autostereoscopic displays, a physical mechanism is typically used to display points of light within a volume. Because volumetric displays are not planar, volumetric displays use voxels instead of pixels. Two exemplary types of volumetric displays include multiplanar displays, which have multiple display planes stacked up, and rotating panel displays, where a rotating panel sweeps out a volume.
Parallax autostereoscopic displays may use barriers or lenticular sheets to produce different two-dimensional images across a viewing field. Parallax autostereoscopic displays operate by occluding certain parts of an image from a particular viewing direction while making other parts visible. They provide different imagery to the left and right eyes of a viewer, allowing for 3D perception of a scene. This is commonly achieved by dividing the horizontal resolution of a display surface behind the parallax barrier among several views.
In addition to single-user parallax barrier-based autostereoscopic displays, some conventional autostereoscopic displays support multiple viewers by providing different views for several possible viewing positions. The primary task of any multi-user autostereoscopic display is to deliver the correct and unique view to each eye of each observer. However, a viewer located at a particular viewpoint of a multi-user autostereoscopic display may receive visual interference from an image intended for a viewer located at a different viewpoint because some of the same display pixels may be viewable from both viewpoints. If multiple viewers see the same pixels behind the barrier from different viewpoints and the same pixels should appear differently when viewed from the different viewpoints, then a conflict occurs. In conventional autostereoscopic displays, the visual conflicts may be localized and can cover large areas of the display, depending on viewpoint position. This allows a single viewer to experience correct 3D views from various positions. Examples of conventional parallax barrier autostereoscopic displays include the Mitsubishi Electronics Research Laboratories (MERL) 3D TV system produced by Mitsubishi Electronics Research Laboratories of Cambridge, Mass. which uses projection display with lenticular elements and the 3D Intelligent Display Solution produced by Philips, Inc. of Amsterdam, Netherlands.
FIG. 1 is a top-view of a conventional multi-user autostereoscopic display illustrating two “repeat” stereoscopic viewpoints and two monoscopic viewpoints. Referring to FIG. 1, conventional AS display system 100 may include display 102 and parallax barrier 104. Display 102 may include a rear-projection or emissive display such as a liquid crystal display (LCD). Display 102 may include an array of pixels, where each pixel is capable of emitting a single frequency of light (e.g., color) at a given point in time. Conventional parallax barrier 104 may include a material capable of blocking light emitted from display 102 from reaching viewers located on the opposite side of barrier 104 from display 102. Conventional parallax barrier 104 may also include a regular pattern of holes allowing for a portion of light emitted from display 102 to be observed by viewers using conventional AS display system 100. For example, in two dimensions, a regular hole pattern may include a grid such that holes are spaced at regular intervals from each other in both the horizontal and vertical directions. However, it is appreciated that for simplicity of illustration, the top-view shown in FIG. 1 includes a regular pattern in one dimension whereby holes are located at regular intervals in only the horizontal direction. This may hereinafter be referred to as a “display scan line.”
One problem associated with conventional multi-user parallax barrier-based AS displays is that, in order to preserve horizontal resolution, such displays have a limited number of distinct views, typically eight to ten. Autostereoscopic displays often require sizing individual views to the scale of the interpupillary distance of a user, approximately 6 cm. At the optimal distance where this spacing occurs, the maximum width of the display's views is, therefore, approximately half a meter. This leads to two fundamental problems for groups of users viewing such an autostereoscopic display. Due to the regular pattern of conventional parallax barriers, each view repeats in front of the display at the regular interval of the view repeat distance. When one viewer is viewing the display in one area, any other viewer must be restricted from entering any of the repeat areas or the other viewer will see the same output as the first viewer when the other viewer should see different output. This severely limits the lateral movement and potential viewing positions for additional viewers.
Another problem associated with conventional AS displays is that the number and location of unique viewpoints that are different distances away from display 102 may also be limited. When a viewer is located close to display 102 and barrier 104, the angles between the light rays transmitted from the viewable pixels and converging on the viewer may be large. As a result, the gaps between pixels viewable through barrier 104 may be large. In contrast to a viewer located close to display 102, the angles between the light rays transmitted from the viewable pixels and converging on a viewer located far away from display 102 may be small. Typically, given the proximity of barrier 104 to display 102 (e.g., centimeters) and the relative distance between a viewer and barrier 104 (e.g., a few meters), light rays transmitted from display 102 that converge on a viewer are virtually parallel. As a result, the spacing between viewable pixels for viewers located at viewpoints that are far away from display 102/barrier 104 is small compared to viewers located closer to display 102/barrier 104. Because the spacing between viewable pixels is smaller for far viewpoints, more pixels are viewable and therefore the sampling frequency is higher (i.e., pixels are sampled more frequently than for viewers located closer to display 102/barrier 104).
For a regular barrier display, a viewer located at a first (calibrated) distance will sample the pixels at a particular frequency corresponding to the correct spacing for the zones. However, viewers located at different distances from the display will sample the display at frequencies that do not correspond to the regular spacing of viewing zone pixels. The superposition of such pixel sets may lead to an undesirable pattern of pixels observable at the two viewpoints simultaneously, no matter what the lateral positions of the viewers. Thus, viewers located at different distances from a regular barrier display may be undesirably restricted to approximately the same distance from the display in order to avoid this undesirable view interference.
For example, in FIG. 1, viewpoint 116 may be located at a first distance from barrier 104 such that a viewer located at viewpoint 116 observes a portion of display 102 through the regular pattern of holes in barrier 104. As shown in FIG. 1, a viewer located at viewpoint 116 may observe display area 106 through a first hole, display area 108 through a second hole, and display area 110 through a third hole. A viewer located at viewpoint 118 may observe a different area of display 102 through the same pattern of holes in barrier 104. The display area viewable by the viewer located at viewpoint 118 may overlap the display area viewable by viewpoint 116, which may result in undesirable visual interference for one or both of viewpoints 116 and 118. Specifically, the viewer located at viewpoint 118 may observe display area 106 through the first hole, display area 112 through the second hole, and display area 114 through the third hole. Because the spacing of the intersections of rays from viewpoint 116 is greater than the spacing of the intersection of rays from viewpoint 118, fewer areas on display 102 are viewable to a viewer located at viewpoint 116 than one located at viewpoint 118. As a result, a viewer located at viewpoint 116 may “sample” display 102 at a lower frequency, while a viewer located at viewpoint 118 may “sample” display 102 at a higher frequency.
Other types of conventional autostereoscopic displays may utilize user tracking systems to provide the correct view for multiple viewpoints. User tracking (e.g., head tracking) relies on finding the position of a person relative to the display and adjusting the display contents to give the illusion of looking through a window into a 3-D environment. Conventional head-tracking systems may use facial and/or head recognition software in order to locate the user in the room. However, the head tracking induced 3D effect only works the person whose head is being tracked and untracked users may not get the same effect. Therefore, with regular barrier, multi-user autostereoscopic displays, untracked users must remain in certain viewing areas or they will see incorrect imagery.
Interference between views may produce a form of aliasing resulting in various undesirable visual artifacts such as jagged edges and/or Moiré patterns. Aliasing is a long recognized problem in computer graphics and solutions include pre- and post-filtering images as well as supersampling. Although filtering methods for antialiasing in autostereoscopic displays have been proposed, these operate on image quality and depth-of-field rather than between views. Moreover, using supersampling to overcome the aliasing problems associated with regular barrier displays is not possible because the barrier pattern fixes the sampling rate of the underlying display.
Yet another limitation of many conventional parallax barrier autostereoscopic displays is low brightness and resolution. For example, a typical eight-view regular parallax barrier display may block ⅞ of the light emitted from the backing display panel or projector, and have only ⅛ of the full horizontal resolution. As a result, viewers of conventional parallax displays may have difficulty reading text or discerning fine details of images. Viewers may also have difficulty observing images in low-light conditions or from larger distances where brightness may be an issue.
Accordingly, in light of these difficulties, a need exists for improved methods, systems, and computer readable media for generating autostereo three-dimensional views of a scene for a plurality of viewpoints.